1. Field of the Invention
The present invention relates to a guiding method for an autonomous travelling vehicle which is provided with a plurality of wheels mounted on both right and left sides, capable of independently rotating themselves.
2. Description of the Prior Art
Conventionally, there are a variety of guiding methods for making an autonomous vehicle, for example, autonomously travel itself. Typically, one of the conventional methods makes an unmanned vehicle travel along continuous routes which are preliminarily set either by guidance cables or by optical tapes and the like. Another conventional system guides an unmanned vehicle by making it identify environments of the travelling route by applying electric waves or light so that it can proceed on its own route in accordance with data thus identified. Another conventional method guides an unmanned vehicle by applying a presumptive navigation method.
However, the method which provides the unmanned vehicle with its route by means of guiding cables unavoidably obliges the investor to spend much expense and time for establishing the route. Actually, once the route is established, it cannot easily be modified or changed. As for an optical tape, due to soil deposited on its surface after continuous service for many years, accuracy for detecting the route of the unmanned vehicle unavoidably decreases. Furthermore, such a conventional method making the unmanned vehicle travel along its route using electric waves or light for identifying the environment of the route easily incurs unwanted interference from external factors, thus lowering the accuracy for correctly detecting the route.
To solve those problems mentioned above, the Japanese Patent Laid-Open No. 57-120118 (1982) proposes a method for guiding a travelling object such as an unmanned vehicle for example, by providing it with information of the route by applying a presumptive navigation method.
This system first detects the distance covered and the turning angle of the unmanned vehicle and then detects the present position and posture angle with respect to the reference point by seeking the sum of the traveling track in accordance with the detected information. Simultaneously, this method sets coordinate XY on the floor on which the vehicle travels as shown in FIG. 1, while it also sets the route C and fixed points P0, P1, P2,--on the route C. Using each of these fixed points for making up the origin, the method sets coordinate xy respectively so that the tangent of each of these fixed points can correctly match the axis y. The position of each fixed point is denoted by applying coordinate xy, the origin of coordinate xy is made of the next fixed point in the proceeding direction of the travelling vehicle. An operator preliminarily sets a specific angle formed with respect the origin as the variable part of the posture angle of fixed points.
More particularly, as shown in FIG. 1, the operator preliminarily sets an angle .theta.m with axis y of the coordinate xy having the next fixed point Pm+1 as the origin against fixed point Pm in order that the angle .theta.m can become a variable part .DELTA..theta.m of the posture angle of the fixed point Pm. While the unmanned vehicle travels, it sequentially seeks the traveling speed and the steerage angle by referring to the present position and the azimuth on the coordinate xy having the next fixed point Pm+1 as the origin, while the vehicle also refers to the deviation angle .theta.m against the origin Pm+1. The unmanned vehicle then subtracts the steerage angle from the variation .DELTA..theta.m of the posture angle which has been read when passing through the fixed point Pm, and then the unmanned vehicle travels in the direction of the origin Pm+1 in order that the variation .DELTA..theta.m can be reduced to zero. In other words, this is one of the origin-pursuing guiding methods for making the unmanned vehicle first read the variation .DELTA..theta.m of the posture angle every time when it reaches the fixed point Pm and then repeats the identical running processes by sequentially renewing the origin Pm+1 in order that it can correctly follow up travelling by being guided throughout the route.
Conventionally, any of those guiding methods using the presumptive navigation method provides means for confirming and correcting for the absolute position of the travelling object, which can be executed in any optional location of the route. Conventionally, a method called "fixed-point correction method" is known, which makes the unmanned vehicle firstly identify the externally provided marks before eventually confirming and correcting for the absolute position of the travelling vehicle itself.
The Japanese Patent Laid-Open No. 51-53870 (1976) proposes a method in conjunction with the presumptive navigation method for detecting the present position and the azimuth of the travelling object, where this invention provides means for allowing the control system of the travelling object to independently count the number of pulses generated by a pair of pulse counters installed on the left and right wheels respectively of the travelling object at every extremely short period of time, and then based on the counted values, the control system computes variation of the average speed and the azimuth of the travelling object before eventually determining the present position and the azimuth of the travelling object.
As is clear from the above description, the guiding method proposed by the invention related to the Japanese Patent Laid-Open No. 57-120118 (1982) obliges the operator to preliminarily and sequentially store data related to the variable values of the posture angle of the travelling object at a number of objective points provided on the routes into memory means, thus involving complex procedures. Furthermore, despite being the guiding method based on the presumptive navigation method, this invention however does not specify means for correcting for guidance error that may take place with the presumption error.
On the other hand, according to the invention related to the Japanese Patent Laid-Open No. 51-53870 (1976), since the present position and the azimuth of the travelling object are detected in accordance with the rotation of wheels, errors can easily be generated by either slipping or noise of these wheels, thus eventually causing deviation to occur to the present position and the azimuth of the travelling object. In addition, since this invention is totally dependent on the externally provided units for identifying error and deviation, this method can only execute rough correction thus unavoidably resulting in the poor guidance accuracy.